The present invention relates to a refrigeration device, and more particularly to a refrigeration device that is capable of both freezing and chilling.
Refrigeration devices that are employed in containers and the like are not only capable of freezing but are also capable of chilling, i.e., maintaining a temperature that is slightly above the freezing point.
In this type of refrigeration device, the compressor must have a sufficiently large freezing capability in order to freeze items in the refrigeration device. On the other hand, there is less demand on the compressor during chilling than there is during freezing because the temperature differential between the outside air and the interior of the refrigeration device is small. Thus, the compressor is stopped during chilling, and this suppresses the capabilities of the refrigeration unit.
However, when the freezing capability of the refrigeration unit is suppressed in this manner during chilling, the compressor is frequently started and stopped in order to control the temperature inside the refrigeration device, and as a result the lifespan of the compressor is shortened. In addition, there will be large changes in temperature when it is controlled by starting and stopping the compressor, and this characteristic is not desirable in a refrigeration unit that is required to maintain a constant temperature.
Because of this, it is desirable that the compressor run as continuously as possible while suppressing the capability of the refrigeration unit. The following means are used to accomplish this. An intake proportional valve is placed on the intake side of the compressor in a refrigeration circuit, and by closing this intake proportional valve, the amount of refrigerant supplied to the compressor can be suppressed. When this is done, the amount of refrigerant in the compressor is reduced, and thus the freezing capability of the refrigeration device is reduced. Thus, the freezing capability of the refrigeration device can be controlled while continuously operating the compressor.
In addition, a thermo-sensitive expansion valve is employed in conventional refrigeration devices. The thermo-sensitive expansion valve has a thermo-sensitive line that is disposed near the outlet of the evaporator, and the temperature of the refrigerant near the outlet of the evaporator is slightly hotter than normal. Because of this, the temperature near the inlet inside the evaporator will be different then the temperature near the outlet. This is because the thermo-sensitive expansion valve places the refrigerant near the outlet in the superheated steam state, but places the refrigerant near the inlet in the wet saturated steam state. Thus, when a thermo-sensitive expansion valve is used as an expansion valve, a temperature distribution will be produced inside the evaporator.
In this situation, because the freezing capability of the refrigeration unit is being controlled during chilling, as noted above, the temperature distribution in the evaporator is largely responsible for creating a temperature distribution inside the refrigeration unit. Because of, this, a non-uniform temperature distribution inside the refrigeration unit will occur easily when a temperature distribution is produced in the evaporator.
It is an object of the present invention to provide a refrigeration device that maintains the temperature inside the refrigeration unit at a stable level when the freezing capability of the refrigeration device is being suppressed.
The refrigeration device according to a first aspect of the present invention is made of a refrigeration circuit, control means, and command means. The refrigeration circuit is sequentially connected to a compressor, a condenser, an electric expansion valve, an evaporator, and an intake proportional valve. The control means controls the capacity of the refrigerant circuit. The command means provides commands to the control means. Furthermore, when the control means receives a request to suppress the capabilities of the refrigerant circuit from the command means, the intake proportional valve will be restricted in order to place the refrigerant in the discharge side of the evaporator in the wet saturated steam state, and the electric expansion valve will be set to an aperture such that the refrigerant in the interior of the evaporator will be placed in the wet saturated steam state.
In this refrigeration device, the intake proportional valve will be restricted by the control means during chilling. When this occurs, refrigerant in the wet saturated state will be collected in the outlet of the evaporator. Thus, the freezing capability of the refrigeration device will be suppressed and chilling will be made possible because the amount of refrigerant circulating in the refrigerant circuit will be reduced.
Furthermore, the interior of the evaporator can be filled with refrigerant in the wet saturated state by setting the aperture of the electric expansion valve such that the refrigerant is in the wet saturated steam state. Refrigerant in the wet saturated state will be at a constant temperature due to the equal pressure inside the evaporator. This allows the temperature of the evaporator to be uniform both when the freezing capability of the refrigeration device is suppressed and when freezing takes place, and makes it difficult to generate temperature irregularities. Thus, the temperature inside the refrigeration device can be maintained at a stable level.
Note that when a thermo-sensitive expansion valve is used conventionally as an expansion valve, the temperature distribution inside the evaporator will not be uniform because the expansion valve will regulate the refrigerant such that it will enter the superheated steam state near the outlet of the evaporator. However, the refrigerant in the evaporator can be placed in the wet saturated state and a uniform temperature distribution inside the evaporator can be achieved because an electric expansion valve is employed in the present invention.
The refrigeration device according to a second aspect of the present invention is the refrigeration device of the first aspect, and further includes a protection means that prevents damage to the compressor.
When the freezing capability of the refrigeration device is suppressed and chilling takes place, there are times when damage to the compressor will occur. For example, when non-compressible liquid refrigerant flows therein, it is possible to damage the compressor when it generates high pressures. Furthermore, the amount of lubricating oil inside the compressor will be reduced, thus making it easy to bum the compressor, because the lubricating oil will be driven out of the compressor by the liquid refrigerant.
Various types of damage to the compressor can be prevented because of the presence of the protection means in the refrigeration device.
The refrigeration device according to a third aspect of the present invention is the refrigeration device of the second aspect, wherein the protection means includes a sensor that detects the pressure and temperature of the refrigerant in the discharge side of the compressor, and will deduce the pressure and temperature of the refrigerant in the intake of the compressor based upon the detection results from the sensor.
A sensor that detects the temperature and pressure of the refrigerant in the discharge side of the compressor is provided as the protection means. The pressure and temperature of the refrigerant in the intake of the compressor will be deduced from the detection results of the sensor. The pressure and temperature deduced therefrom will be used to, for example, regulate the electric expansion valve and the intake proportional valve, and to prevent the refrigerant in the intake of the compressor from entering the liquid state. This will prevent damage to the compressor.
The refrigeration device according to a fourth aspect of the present invention is the refrigeration device of the second aspect, in which the protection means includes an oil temperature sensor that detects the temperature of oil in the compressor, and will deduce the degree of wetness of the refrigerant in the intake of the compressor based upon the detection results from the oil temperature sensor.
Here, the degree of wetness of the refrigerant in the intake of the compressor will be deduced from the detection results from the oil sensor serving as the protection means. The pressure and temperature deduced therefrom will be used to, for example, regulate the electric expansion valve and the intake proportional valve, and to prevent the refrigerant in the intake of the compressor from entering the liquid state. This will prevent damage to the compressor.